This application claims the benefit of a Japanese Patent Application No.2002-246912 filed Aug. 27, 2002, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to, and more particularly to code conversion apparatuses, code conversion methods and storage media, and more particularly to a code conversion apparatus and a code conversion method for converting coded image information, and to a computer-readable storage medium which stores a computer program for causing a computer to carry out such a code conversion of the coded image information.
2. Description of the Related Art
It is anticipated that the demands to further improve the performance and multi-functions of the image compression and expansion techniques for facilitating the processing of high-definition still images will continue to increase. Presently, the Joint Photographic Experts Group (JPEG) is most popularly used as the image compression and expansion algorithm for facilitating the processing of the high-definition still images. In addition, the use of the Discrete Wavelet Transform (DWT) in place of the Discrete Cosine Transform (DCT) which is used by JPEG, is increasing. The image compression and expansion technique called JPEG2000 is a typical example, which has become an international standard in 2001 to succeed the JPEG.
There are various forms of use and states of use of the image data which is subjected to the compression and expansion by the JPEG2000 or the like. For example, an image file provider (or manager) may provide image files to the user via the Internet on an accounting (or charging) system basis. In this case, the image file is distributed in the form of a sample image for confirmation, and the size and/or the resolution of this sample image is intentionally reduced so as not to enable complete viewing of the image file. The actual image file having the enlarged size and/or high resolution is distributed to the user only after the user purchases the image file by viewing the sample image. Moreover, the image which may be displayed on a display device of a terminal may be restricted by the performance of the display device. In this case, an original full-color image may only be displayed on the display device as a monochrome image or, the size and/or the resolution of the original image may only be displayed on the display device with a reduced size and/or resolution, due to the limited performance of the display device.
Therefore, although the JPEG2000 is a compression and expansion technique which can send the original image with a high reproducibility, the expansion (or decoding) of the original image in the original form may not always be desired, depending on the purpose or usage of the image data.
For example, suppose that a code A which is obtained by compressing a first image is to be converted into a code B which is obtained by compressing a second image having ½ the resolution of the first image, where the first and second images relate to the same image but have mutually different resolutions. In general, this conversion may be realized by a procedure which (i) expands (decodes) the code A, (ii) converts the resolution of the decoded image, and (iii) compresses (encodes) the decoded image having the converted resolution into the code B. However, such a procedure requires a troublesome and time-consuming process. In addition, unnecessary picture quality deterioration may be introduced due to-an inverse quantization or the like which are required by the procedure. Furthermore, since the decoded image having the converted resolution needs to be compressed (encoded) again, this compression may be different from the compression which is carried out with respect to the first image when obtaining the code A, and it may become impossible to expand (decode) the code B back into the original first image.
Accordingly, the present inventors have found that it would be convenient if it is possible to create the code B by simply editing the code A in the encoded state, because this would not require the encoding and decoding and thereby shorten the processing time, and would not require the inverse quantization and thereby prevent unnecessary picture quality deterioration. Moreover, the present inventors have found that it would be more convenient if the original code A can be restored by simply editing the code B in the encoded state, since this would have the effect of concealing a portion of the code A from the user.
The DWT may also be regarded as a method of converting the resolution into 2n having a high picture quality, and methods of obtaining from the code an image having a lower resolution that the original image have been proposed in Japanese Laid-Open Patent Applications No.2000-125293 and No.2000-125294, for example. The Japanese Laid-Open Patent Applications No.2000-125293 and No.2000-125294 not only describe the methods of converting the resolution into 2n, but also describe the methods of converting the resolution into an arbitrary resolution. But the methods proposed in the Japanese Laid-Open Patent Applications No.2000-125293 and No.2000-125294 are applied to cases where the user himself desires to convert the resolution, and it is originally possible to decode the code back into the original image. For this reason, these proposed methods are unsuited for application to an accounting system, such as that described above where the provider of the image data desires to intentionally convert the resolution or the like when providing the data to the user.
Various methods, including the proposed methods described above, have been proposed to reduce the resolution or the size of the image. However, not much research has been made on methods of generating an image having a resolution higher than that of the original image, probably because it is conceivable to carry out an interpolation after decoding of the code, by an existing interpolation method such as the cubic convolution method which is a kind of third order interpolation method. However, in the individual apparatus which processes the image, the picture quality obtainable by the algorithm used for the interpolation may be insufficient. Such a situation occurs when the interpolation algorithm is limited to the simple nearest neighbor method, and not the cubic convolution method, due to priority placed on the computation speed.
Accordingly, the present inventors have found that it would be convenient if it is possible to simply enlarge the size and/or increase the resolution of the image in an existing apparatus having the basic structure of the JPEG2000, and not having a high-speed and high-performance processing circuit which uses the cubic convolution method as the third order interpolation method.